Exclusive checkbox doesn't work

Hi,

I have a problem to get exclusive checkboxes to work on my development site. I have for example added the following code:
[checkbox* question-1 class:custom-check use_label_element exclusive “Dåligt” “Mindre bra” “Okey” “Ganska bra” “Mycket bra”]

but it doesn’t show up as exclusive on this page:
http://interimschef.nu/utvardering/

I have googled and tried to find any answer on various forums, but couldn’t find anything. Please advice!

Cheers,
Henrik

https://ww.wp.xz.cn/plugins/contact-form-7/